1. Field of the Invention
The present invention relates to a heat spreader formed to be insert-moldable so that part thereof is embedded in mold resin, and a semiconductor device in which a semiconductor chip mounted onto a circuit board is insert-molded with mold resin together with the above-mentioned heat spreader. This invention also relates to a method for manufacturing such a semiconductor device.
2. Description of the Related Art
A semiconductor device of a molded BGA (ball grid array) type is formed in such a manner that a semiconductor chip is mounted onto one surface of a single- or multiple-layered circuit board on which circuit patterns are formed, and is electrically connected to the circuit patterns, after which the circuit board is set in a mold to shield the semiconductor chip with mold resin. Then, solder balls are placed on lands formed on the opposite surface of the circuit board, and bonded thereto by reflow.
Recently, the working frequency of a microprocessor unit (MPU) mounted onto an electronic equipment such as a personal computer has become higher whereby a large amount of heat is generated from a semiconductor chip and a chip set in the vicinity thereof. To enhance the heat dissipation from the semiconductor device, one semiconductor device has been proposed which is produced by the insert-molding of a so-called mold-insertion type heat spreader with mold resin. More concretely, the heat spreader is preliminarily placed within a cavity of a mold, and a circuit board on which a semiconductor chip is mounted is placed in the cavity, after which the mold is clamped and shielded with resin. Thereby, a semiconductor device in which the heat spreader is molded while being exposed outside a package part is obtained. The semiconductor device in which the heat spreader is insert-molded with mold resin is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 7-321246 or U.S. Pat. No. 5,216,278.
To enhance the heat dissipation, the mold-insertion type heat spreader covers a top surface of the semiconductor chip, and it is necessary that an area or volume occupied by the package part is larger. Also, to facilitate the reliability of the semiconductor device, it is necessary to bring the heat spreader into tight contact with the semiconductor chip. Otherwise, to enhance the mold quality and the productivity, it is necessary to improve the pouring efficiency of mold resin. That is, since the package part is thin, the mold resin must shield a relatively wide area through a narrow space between the circuit board and the heat spreader. If voids generate due to the involvement of air or the fluidity of mold resin is unfavorable, there may be a problem in that the mold resin solidifies before it is sufficiently spread throughout the package.
Further, it is desirable that the heat spreader can be easily assembled and is good-looking when being exposed out of the resin-molded package as well as allowing the semiconductor device to be produced at a lower cost.
An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a heat spreader improved in the heat dissipation and close adherence with the mold resin as well as being excellent in pouring efficiency of the mold resin, and a semiconductor device having a high reliability and high productivity incorporating such a heat spreader.
According to the present invention, there is provided a heat spreader adapted to be insert-molded with resin on a surface of a circuit board on which a semiconductor chip is mounted so that said heat spreader covers said surface of the circuit board including an upper surface of said semiconductor chip over substantially a same area as that covered with molded resin when insert-molded with resin, said heat spreader having: a first, main portion which defines a first gap with respect to said surface of the circuit board when insert-molded with resin; and a second portion which defines a second gap with respect to said surface of the circuit board when insert-molded with resin, said second gap being smaller than said first gap, so that at least said second portion is embedded in said mold resin when insert-molded with resin.
According to another aspect of the present invention, there is provided a heat spreader adapted to be insert-molded with resin on a surface of a circuit board on which a semiconductor chip is mounted so that said heat spreader covers said surface of the circuit board including an upper surface of said semiconductor chip over substantially a same area as that covered with molded resin when insert-molded with resin,
said heat spreader comprising: a first (lower) surface positioned at a side of said circuit board and adhered with resin when insert-molded with resin; and a second (upper) surface positioned opposite to said first surface and at least a part thereof defining an exposed surface when insert-molded with resin;
said heat spreader further comprising: a first part, at the first surface thereof, defining a first gap with respect to said surface of the circuit board when insert-molded with resin and, at the second surface thereof, defining said exposed surface when insert-molded with resin; and a second part, at the first surface thereof, defining a second gap with respect to said surface of the circuit board when insert-molded with resin, said second gap being smaller than said first gap and, at the second surface thereof, being adhered to and embedded in resin when insert-molded with resin.
The heat spreader further comprises a plurality of third parts (legs), at the first surface thereof, which are in contact with said surface of the circuit board when insert-molded with resin. The third parts are provided on said second part.
The heat spreader further comprises, in a plan view thereof in parallel to said surface of the circuit board when insert-molded with resin: a central region recessed toward said surface of the circuit board to define a recessed portion constituting at least a part of said second part; and said recessed portion comprising a bottom portion provided with at least one resin hole through which resin flows when insert-molding and a peripheral portion provided with at least one ventilation hole through which air is ventilated when insert-molding; and said recessed portion, at the second surface thereof, being adhered to and embedded in resin when insert-molded with resin.
The heat spreader comprises, in a plan view thereof in parallel to said surface of the circuit board when insert-molded with resin: an outer peripheral region stepped toward said surface of the circuit board to constitutes at least a part of said second part along all over an outer periphery thereof; and said outer peripheral region, at the second surface thereof, being adhered to and embedded in resin when insert-molded with resin.
Otherwise, the heat spreader comprises, in a plan view thereof in parallel to said surface of the circuit board when insert-molded with resin: a central region recessed toward said surface of the circuit board to define a recessed portion constituting at least a part of said second part, and said recessed portion comprising a bottom portion provided with at least one resin hole through which resin flows when insert-molding and a peripheral portion provided with at least one ventilation hole through which air is ventilated when insert-molding; and said recessed portion, at the second surface thereof, being adhered to and embedded in resin when insert-molded with resin; an outer peripheral region stepped toward said surface of the circuit board to constitutes at least a part of said second part along all over an outer periphery thereof; and said outer peripheral region, at the second surface thereof, being adhered to and embedded in resin when insert-molded with resin; and an intermediate region between said central region and said peripheral region, at the second surface thereof, defining an exposed surface when insert-molded with resin.
The heat spreader further comprises, when insert-molding with resin: means for defining a first cavity between said first surface of this heat spreader and said surface of the circuit board and means for defining a second cavity between said second surface of this heat spreader and an insert mold frame which is in contact with said first part, at the second surface thereof, and with a peripheral edge of said heat spreader; and both said first and second cavities being filled with resin when insert molded, and a volume of said first cavity is larger than a total volume of said second cavity.
According to still another aspect of the present invention, there is provided a semiconductor device comprising: a circuit board having a surface; a semiconductor chip mounted on said surface of the circuit board; and a heat spreader having a first, main portion which defines a first gap to said surface of the circuit board, and a second portion which defines a second gap to said surface of the circuit board, said second gap being smaller than said first gap; and a resin insert-molded with said heat spreader integrally on said surface of the circuit board so as to cover an area of said surface including an upper surface of said semiconductor chip, so that at least said second portion is embedded in said resin.
According to a further aspect of the present invention, there is provided a semiconductor device comprising: a circuit board having a surface; a semiconductor chip mounted on said surface of the circuit board; and a heat spreader insert-molded with resin on a surface of a circuit board so that said heat spreader covers said surface of the circuit board including an upper surface of said semiconductor chip over substantially a same area as that covered with molded resin;
said heat spreader comprising: a first (lower) surface positioned at a side of said circuit board and adhered with resin; and a second (upper) surface positioned opposite to said first surface and at least a part thereof defining an exposed surface;
said heat spreader further comprising: a first part, at the first surface thereof, defining a first gap with respect to said surface of the circuit board and, at the second surface thereof, defining said exposed surface; and a second part, at the first surface thereof, defining a second gap with respect to said surface of the circuit board, said second gap being smaller than said first gap and, at the second surface thereof, being adhered to and embedded in resin; and said resin insert-molded with said heat spreader integrally on said surface of the circuit board so as to cover an area of said surface including an upper surface of said semiconductor chip, so that said second part of the heat spreader, at the first surface thereof, is adhered to and embedded in said resin.
According to still further aspect of the present invention there is provided a method for manufacturing a semiconductor device; said device comprising a semiconductor chip mounted on said surface of the circuit board; and a heat spreader insert-molded with resin on a surface of a circuit board so that said heat spreader covers said surface of the circuit board including an upper surface of said semiconductor chip over substantially a same area as that covered with molded resin, said heat spreader comprising: a first surface positioned at a side of said circuit board and adhered with resin; and a second surface positioned opposite to said first surface and at least a part thereof defining an exposed surface; and said heat spreader further comprising: a first part, at the first surface thereof, defining a first gap with respect to said surface of the circuit board and, at the second surface thereof, defining said exposed surface; and a second part, at the first surface thereof, defining a second gap with respect to said surface of the circuit board, said second gap being smaller than said first gap and, at the second surface thereof, being adhered to and embedded in resin:
said method comprising:
setting a molding component to define a mold cavity comprising a first cavity between said first surface of this heat spreader and said surface of the circuit board and a second cavity between said second surface of this heat spreader and said components, so that at least a part of said molding components is in contact with said first part, at the second surface thereof, and at least a remaining part of said molding component is in contact with a peripheral edge of said heat spreader; and
injecting resin simultaneously into both said first and second cavities so that both said first and second cavities are filled with resin.